1. Field of the Invention
The invention relates to tools for cold forming parts from metallic blanks by revolution, in particular for forming grooves or a knurling.
2. Discussion of Background Information
“Cold forming” means a deformation of the metal of the blank at ambient or semi-hot temperature (up to a temperature of 300–500° C. depending on the metal of the blank), below its melting point.
To form the part from a blank, one generally proceeds according to a so-called “penetration step” during which the blank is engaged with at least one (generally two) forming tool. This penetration step is followed by a second so-called “calibration step” during which the blank is finally calibrated to the desired dimensions for the formed part. During these two steps; the blank is displaced in a relative rotation with respect to the tool, while maintaining the blank under pressure against the tool.
The useful surface of the tool has a plurality of trapezoidal or prismatic teeth having straight or curvilinear sides, and capable of forming grooves or other desired part profile. The teeth of the tool are regularly spaced over a surface of the tool called the “tooth gullet.” They can have different heights in relation to the tooth gullet. The tooth gullet itself can have a variable height in relation to a forming reference axis or plane on the tool, which usually defines the positioning and/or displacement of the tool in relation to the blank to be formed.
These variations in height define the overall profile of the tool, which generally has a first zone, so-called “penetration zone,” for the first step, followed by a second zone, so-called “calibration zone,” for the second step. In known tools, the penetration zone has teeth, the height of which increases with respect to the forming reference axis. During the displacement of the blank in relation to the tool, a slip may occur due to a loss of contact between the surface of the blank to be formed and the tips of the first teeth of the tool. Furthermore, the Applicant has noted a frequent wear on the first teeth.